The present invention relates to the field of illuminated signs. More particularly, the present invention provides illuminated signs including partially transmissive lamp masks.
Illuminated signs, sometimes referred to as light boxes, are often used to enhance the presentation of images and/or text. Examples of illuminated signs can be found in, e.g., airports, mass-transit stations, shopping malls and other public places. The signs typically include an enclosure having an illuminated face over which a graphic (including images and/or text) is located. The illumination is typically provided by an array of elongated fluorescent lamps located behind the sign face and within the enclosure. The images and/or text in the graphic typically include transparent or translucent portions to enhance their visibility when placed over the illuminated face.
In most situations, it is desirable that the sign have a face that exhibits substantially uniform illumination over its entire surface. In conventional illuminated sign design, the thickness of the sign enclosure is controlled by the distance of the centers of the lamps from the sign face. The distance of the lamps from the sign face is, in turn, controlled by the distance between the lamps within the sign. The industry standard lamp spacing ratio required to provide sufficient, uniform illumination is 2:1, i.e., the distance between adjacent lamps is about twice the distance from the lamp centers to the sign face. In many conventional signs, this ratio yields illuminated signs with an overall thickness of about 4 inches (10 cm) and a lamp spacing of about 5-6 inches (13-15 cm).
Spacing the lamps in a conventional sign farther apart than is discussed above can result in non-uniform illumination, i.e., portions of the face will be significantly darker or brighter than others. Those non-uniformities can detract from the graphic located on the sign face.
In many cases the thickness of the illuminated signs can be problematic. For example, the signs may protrude out from a wall far enough to create a potential hazard. In some public locations, the distance by which signs may protrude from a wall surface is regulated to, e.g., 4 inches (11 cm) or less.
One potential approach to reducing illuminated sign thickness is to place the lamps closer together. As a result, the distance from the lamp centers to the sign face can be reduced (using. e.g., the 2:1 ratio discussed above). One significant drawback to this approach is, however, that the costs of operating the sign are also increased.
Furthermore, placing the lamps closer together may result in unacceptable increases in luminance of the sign face. Signs that are too bright may detract from the presentation of the graphics placed on them. For example, a commonly accepted range of luminance for outdoor illuminated signs is about 100-300 Footlamberts (340-1030 Candela/m2). Exceeding this range may result in a sign that is unacceptably bright and washed outxe2x80x94in addition to requiring additional energy to operate.
The present invention provides an illuminated sign system that provides uniform illumination over the lamp face by using partially transmissive lamp masks located between the lamps and the sign face. The sign face itself also diffusely reflects a majority of light incident on its second surface back towards the interior of the sign. The combination of a diffusely reflective lamp face and partially transmissive lamp masks enhances uniformity of the sign face illumination.
One advantage of illuminated signs manufactured according to the present invention is that the lamp spacing ratio can be increased, e.g., to a ratio of 3:1 or more, and, possibly, to a ratio of 4:1 or more. Surprisingly, these increases in the lamp spacing ratio can be employed with an actual increase in illumination uniformity and while maintaining acceptable brightness.
In one aspect, the present invention provides an illuminated sign including a face having an interior surface facing an interior of the sign and an exterior surface facing away from the interior of the sign, wherein the face diffusely reflects a majority of light incident on the interior surface of the face; a back located opposite the face, wherein the back includes a back surface oriented towards the face, wherein the back surface diffusely reflects a majority of light incident on the back surface; a plurality of lamps located between the face and the back, wherein the lamps and the face are located with a lamp spacing ratio of about 3:1 or more; and a lamp mask located between each of the lamps and the face, wherein each lamp mask transmits only a portion of light incident thereon from its respective lamp.
In another aspect, the present invention provides an illuminated sign including a face having an interior surface facing an interior of the sign and an exterior surface facing away from the interior of the sign, wherein the face diffusely reflects a majority of light incident on the interior surface of the face; a back located opposite the face, wherein the back includes a back surface oriented towards the face, wherein the back surface diffusely reflects a majority of light incident on the back surface; a plurality of lamps located between the face and the back; and a lamp mask located between each of the lamps and the face, wherein each lamp mask diffusely transmits about 20% or less of light incident thereon from its respective lamp.
In another aspect, the present invention provides an illuminated sign including a face having an interior surface facing an interior of the sign and an exterior surface facing away from the interior of the sign, wherein the face diffusely reflects about 80% or more of light incident on the interior surface of the face; a back located opposite the face, wherein the back includes a back surface oriented towards the face, wherein the back surface diffusely reflects about 90% or more of light incident on the back surface; a plurality of lamps located between the face and the back, wherein the lamps and the face are located with a lamp spacing ratio of about 3:1 or more; and a lamp mask located between each of the lamps and the face, wherein each lamp mask diffusely transmits about 20% or less of light incident thereon from its respective lamp over an attenuation arc of about 180xc2x0 or less.
As used in connection with the present invention, xe2x80x9clightxe2x80x9d means electromagnetic radiation in wavelengths that are typically visible to the unaided human eye.
The reflective and transmissive properties of the various components of the signs of the present invention are measured using light approaching the surface of the component at a 90xc2x0 angle to that surface. Such light will be referred to herein as xe2x80x9cnormal incident light.xe2x80x9d Furthermore, the reflective or transmissive values recited are average values over the wavelength range of 500-600 nanometers.
xe2x80x9cInterior lightxe2x80x9d as used in connection with the present invention means light that is located within the interior of the sign, i.e., between the face and back of the sign.
These and other various features and advantages of the invention are described below with reference to various illustrative embodiments of the invention and examples of the invention.